Strange messages displayed alongside actions

[uchwings]

When a user joins a Slack channel, I see two IRC lines of the following form:

* userfoo has joined #my-chan.
<userfoo> @ has joined the channel

The first of these is an IRC JOIN message as expected, but the second is a PRIVMSG that seems to be synthesized by matterircd. This second message is redundant and misleading, since the JOIN line contains the same information and userfoo never typed "@ has joined the channel".

[42wim]

No, it's not synthesized by matterircd, slack sent this message everytime a user joins.
The @ seems a bug though

[42wim]

I'll see if I can surpress the "has joined" message

[liskin]

The @ also sometimes happens when one user mentions another, as in:

16:11:02 < hanule:#general> @ I can take it for you, leaving Saturday :slightly_smiling_face:
instead of
16:11:02 < hanule:#general> @Sheila I can take it for you, leaving Saturday :slightly_smiling_face:

I haven't recognized any pattern in it yet, though. :-/